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• <br />0 <br />INFILTRATION BMPS <br />T5.15 Permeable Pavements <br />Project submission requirements include submitting results of infiltration (Ksat) testing, groundwater <br />elevation testing (or other documentation and justification for the rates and hydraulic restriction layer <br />clearance) with the justification for the feasibility decision regarding permeable pavement, and as <br />justification for assumptions made in the runoff modeling. <br />BMP T5.14A - Rain Garden <br />The top of the ponded surface area below the overflow shall be at least 5% of the total hard surface area <br />draining to the rain garden. If lawn/landscaped areas will also be draining to the rain garden, it is <br />recommended that the top of the ponded surface area below the overflow be increased by 2% of the <br />lawn/landscaped area. The table below provides rain garden geometry based upon contributing area. Refer <br />to the Rain Garden Handbook for Western Washington: A Guide for Design, Installation, and Maintenance <br />(Hinman et.al. 2013) for construction guidance. Rain gardens shall be designed in accordance with the <br />SWMMWW. <br />2:1 <br />800 or less <br />40 <br />0.11 <br />50 <br />2:1 <br />1400 or less <br />70 <br />0.13 <br />110 <br />3:1 <br />3000 or less <br />150 <br />0.06 <br />235 <br />■ Hard surface area requiring mitigation (ft2): <br />■ Lawn/landscape contributing area (ft2): <br />■ Total contributing area (ft2): <br />Top of Ponded Surface Area (ft2) = 0.05*(total hard surface area (ft2)) + 0.02*(lawn/landscape area (ft2)) <br />= 0.05*(------.... _ ft2) + 0.02*(-------..... ft2) <br />ft2 <br />City of Everett Public Works <br />Small Project Stormwater Site Plan Report -Dec 2019 41 <br />